Garden Office Guide: Foundations


There is a lot of choice these days when it comes to garden office foundations, a few years ago your only option was to have a concrete slab base which the customer normally had to organise themselves, today the foundation is normally included in the cost of the garden office.

The types of foundations used in garden office construction include:

Concrete Slab

The original type of concrete foundation a concrete slab forms a sound level base for a garden office. Concrete slabs have gone out of fashion with designers because the site needs to be level, they take a good degree of skill to lay, they need time to ‘go off’ before the garden office can be installed and because they use a lot of concrete they’re not very environmentally friendly. Concrete slabs foundations are normally 100mm thick and approximately 50mm bigger than the garden office to allow for tolerances.

Pile & Pad Foundations

Concrete pile/ pad foundations form the basis of most of the newer foundation systems used in garden office design. A number of concrete piles/pads are evenly spaced in the footprint area of the garden office. Garden office suppliers normally use a power auger to dig the holes whilst some may use a spade! The depth of the hole depends on the soil conditions as the foundation needs to sit in solid ground. Some companies use cardboard formers into which they pour the concrete whilst other companies pour the concrete straight into the hole. The piles/pads are then levelled off, the way the foundation is finished varies from supplier to supplier, but these are typical methods:

  • Metal Anchors

These anchors are inserted into the concrete as it sets; anchors are normally height adjustable so that the floor frame can be easily levelled.

  • Concrete Beams

Some suppliers use reinforced concrete beams to connect the concrete piles/pads together, the floor frame sits on top of these beams. The beams are fixed to the piles/pads with galvanised straps and the beams spread the load between the piles/pads.

  • Jacks

Jacks rather like those used to lift a car when changing a tyre are fixed to the concrete piles/pads, the floor frame is then fixed to the top of the jack and it can be levelled easily by turning the screw on the jacks.

  • Timber Bearers

Some supplier connect the concrete piles/pads with timber bearers, the timber floor frame then sits on these bearers. It is important that the timber used for bearers is tantalised.

  • Adjustible Steel Frame

A few suppliers have designed steel frameworks which have adjustable feet which sit on the concrete pads, these frames are easy to level, and the installers just adjust the screw which raises or lowers the frame.

  • Timber Bearers

Some supplier connect the concrete piles/pads with timber bearers, the timber floor frame then sits on these bearers. It is important that the timber used for bearers is tantalised.

  • Metal Grids

Some suppliers have designed a metal grid work system which acts as both the foundation and the floor structure, the grid work has feet which sit on the concrete piles/pads and lifts the garden office off the ground. Several of these grid work panels are joined together to match the size of the garden office and then composite floor panels are slotted into the spaces in the grid.

Screw Piles

Screw piles are a concrete free form of foundation, large ‘screws’ are driven into the ground, this type of foundation is quick to install and can be easily removed from the site if the garden office is ever removed. Because there is no concrete to set the garden office can be installed as soon as all the screw piles have been fitted.

Plinth Foundations

Plinth foundations are very popular in garden office construction, there are two popular systems one involves recycled concrete pads and the other system is made from recycled plastic pads. Both systems work in much the same way – the site is cleared from vegetation and a plastic grid is laid level and filled with aggregate, the pad stones are then laid in the centre of the grid, the height can be adjusted to account for site levels by using incremental packers, the top stone has an adjustable bracket which takes the timber floor frame. The beauty of this system is that the foundation can be installed quickly, there are no wet trades and the foundation can be removed and reused if the garden office is ever removed from the site, it’s also totally recyclable at the end of its life.

Steel Frame

A steel frame goes around the perimeter of the garden office; the frame is fixed to uprights which are set in concrete. The steel frame is designed to take timber floor frames and the load of the building is spread through the steel framework.


Some suppliers use treated sleepers to form the foundation of their garden offices, these are normally laid onto level ground over a damp proof membrane, the sleepers are either used as counter bearers and the floor frame sits on top of them or they from a perimeter frame with joists hanging from them creating a suspended floor.

Paving Slabs

A few garden office suppliers recommend paving slabs as the basis for a garden office, the theory is that a garden office can be situated on an existing patio, we don’t advocate this type of foundation as we don’t consider it strong enough for a garden office – how can slabs you put down for a table and chairs possible have a strong enough basis for a heavy garden office?

There’s a lot of choice out there! Remember don’t stint on your foundation system, go for the best you can afford – you’re garden office is only as good as the foundation it sits upon!

In the next chapter of this guide we look at floors in the Garden Office Guide: Floors

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